1. Field of the Invention
The present invention relates to high-voltage transformers and especially to those used in ignition systems for internal combustion engines. More particularly, the present invention relates to tubular winding forms or bobbins for the secondary windings of an ignition transformer wherein the primary windings and the ferromagnetic core are located within the winding form.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
High-voltage transformers for ignition systems in modern internal combustion engines generally include a tubular winding form that receives a ferromagnetic core (generally of a laminated construction), primary winding surrounding the core and secondary windings wrapped around the winding form. The transformers generally capable of producing a secondary voltage of around 30 KV or more.
The winding form usually has a plurality of axially spaced annular partitions that define annular chambers therebetween. The turns of the secondary windings are wound in the first chamber at one end until the chambers build to a desired level. Then, the windings proceed to the next chamber such as by passing the wire through a helical transition slot formed in the respective partition and then filling the next adjacent chamber to the same level. This process is continued until all of the chambers are filled progressively from one end to the other. The actual winding of the secondary coil is usually accomplished with automatic coil winding equipment.
In modern ignition systems, higher energy coils and spark gaps are being used (e.g. such as in the range of 0.05 inches and higher) in order to achieve better ignition of the fuel. As a result, higher sparking voltages are necessary, such as voltage in excess of 30 KV. The ignition coils are the subject to much greater voltage stress than in the past.
In order to accommodate this, several coils are used in the system, such as one coil for every one or two spark plugs. In the two spark plug configuration, one end of the secondary coil is connected to one plug and the opposite end is connected to the other plug which is set to fire at an opposite portion of the engine cycle.
One problem that can occur during operation of modern automotive ignition systems is sparking across adjacent coil turns during collapse of the transformer field at the firing point. The firing or arcing across the spark gap of the plug generates an RF voltage that may be reflected back to the secondary coil. This high voltage transient or spike may have a frequency of around 10 MHz. The resulting RF energy is quickly dissipated in the first three or four turns of the secondary coil, however, the high RF voltage does present a danger of arcing in the first few turns of the closely coupled wire. In fact, arcing from one end turn to the next frequently does occur, resulting in deterioration of the insulation on the conductor and of the dielectric material in which the conductor is embedded. This can also occur on those coil-on/over plug-type coil assemblies.
Testing has been accomplished on these coil ignition systems in nitrogen atmosphere pressure vessels under conditions that simulate actual engine operation and with the voltage level adjusted to provide optimum sparking. The tests verify that the RF voltage spikes generated causes deterioration of the insulation of the first few turns of the coil and thus premature coil failure. The frequency and magnitude of the reflected RF signal is a function of the sparking voltage and the size of the spark gap.
It is been suggested that a solution to this problem is to enlarge the secondary coil form or bobbin to provide greater spacing between the end turns. The spacing should be sufficient to eliminate arcing. While this may be an effective solution, the enlargement of the coil form is often not possible because of the criticality of the various components of the engine compartment of the vehicle and, in particular, the ignition system components.
In the past, various patents have issued relating to such winding forms. For example, U.S. Pat. No. 4,580,122, issued on Apr. 1, 1986 to P. Worz, describes an ignition coil for ignition systems of internal combustion engines. In particular, the secondary winding and the coil body carrying the ignition coil are manufactured in a chambered realization. The radial extension (i.e. height) of each chamber winding decreases toward the higher chamber potential in accordance with the law of geometric progression so that the insulating distance between the secondary winding and the areas of the ignition coil that carry a lower potential increases with an increasingly higher chamber potential.
U.S. Pat. No. 4,684,912, issued on Aug. 4, 1987 to Kiltie et al., describes a winding form for a high-voltage transformer. This winding form includes a ferromagnetic core, a primary coil and a secondary coil. The secondary windings are wrapped on a tubular insulating winding form or bobbin with annular radial portions defining a plurality of annular coil chambers including a plurality of central chambers and at least one end chamber. The end chamber defines a spiral land that proceeds both axially toward the respective end and radially outwardly for three or more complete turns. The respective end turns of the coil wrap one turn of coil on each turn of the spiral land so that successive turns of the end portions of the secondary coil are both axially and radially spaced from one another sufficient to minimize arcing.
U.S. Pat. No. 5,938,143, issued on Aug. 17, 1999 to K. Yukitakae, shows an ignition coil winding method for spirally winding an element wire in conical banks of wire turns one by one around the coil bobbin. In particular, a nozzle is provided that can vertically move toward and away from the coil bobbin accordingly changing the winding radius and can swing in the direction normal to the longitudinal axis of the bobbin to maintain constant tension of the element wire.
U.S. Pat. No. 6,417,752, issued on Jul. 9, 2002 to Heritier-Best, shows an ignition coil of the type intended to be mounted on a spark plug for the individual electrical supply of the spark plug. This ignition coil includes an internal secondary winding, an external primary winding, a flux return shell, and a casing. The casing surrounds only the secondary winding. The primary winding is wound onto the casing on the outside of the casing. The flux return shell surrounds the casing.
U.S. Pat. No. 7,969,268, issued on Jun. 28, 2011 to Dal Re et al., provides an ignition coil configured for electrical communication with a spark plug of an internal combustion engine. The ignition coil has a primary spool and a secondary spool. The primary spool has a bore and an outer surface with a low-voltage winding supported thereon. The secondary spool has a cavity with a magnetic core received therein at a substantially cylindrical outer surface. The secondary spool is received at least partially in the bore of the primary spool. A high-voltage winding is supported on the outer surface of the secondary spool. The high-voltage winding has discrete winding sectors spaced from one another along the length of the secondary spool.
U.S. Patent Publication No. 2003/0106956, published on Jun. 12, 2003 to Moga et al., teaches a coil winding system for making a secondary winding of an automotive ignition coil. The system includes a roller configured to apply a folding force to the wire being dispensed from a wire nozzle onto a bobbin. The nozzle and the roller are removed by a drive mechanism under control of a controller from one axial end to the other axial end of the bobbin for winding the bobbin in a progressive winding fashion. The roller allows an increase in the winding angle of the layers so as to reduce the voltage difference between adjacent layers and thus reduce incidence of dielectric breakdown in that region.
It is an object of the present invention to reduce and/or eliminate arcing in the end turns of the secondary windings of a combustion engine ignition transformer.
It is another object of the present invention to minimize the possibility of such arcing without changing the dimensional parameters of the secondary windings of the transformer or of the coil form or winding form.
It is another object of the present invention to provide an ignition coil which avoids deterioration of the insulation on the conductor and the dielectric on which the conductor is embedded.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.